Virtual Event: Threat Detection and Incident Response Summit - Watch Sessions
Connect with us

Hi, what are you looking for?

SecurityWeekSecurityWeek

Vulnerabilities

Microsoft Urges Customers to Patch Recent Active Directory Vulnerabilities

Microsoft on Monday released an alert on two Active Directory vulnerabilities addressed with the November 2021 Patch Tuesday updates, urging customers to install the available patches as soon as possible, to prevent potential compromise.

Microsoft on Monday released an alert on two Active Directory vulnerabilities addressed with the November 2021 Patch Tuesday updates, urging customers to install the available patches as soon as possible, to prevent potential compromise.

Tracked as CVE-2021-42287 and CVE-2021-42278, the two security errors can be chained to impersonate domain controllers and gain administrative privileges on Active Directory.

Proof-of-concept code exploiting the two bugs has been public for more than a week, and Microsoft is warning companies of potential malicious attacks, while also sharing a guide to help organizations identify suspicious behavior exploiting the flaws.

“When combining these two vulnerabilities, an attacker can create a straightforward path to a Domain Admin user in an Active Directory environment that hasn’t applied these new updates. This escalation attack allows attackers to easily elevate their privilege to that of a Domain Admin once they compromise a regular user in the domain,” Microsoft explains.

CVE-2021-42278 is a security bypass vulnerability where attackers can employ computer account sAMAccountName spoofing to impersonate a domain controller.

sAMAccountName attributes, Microsoft notes, usually have “$” at the end of their names, which is meant to help distinguish between user and computer objects. Because of the bug, a normal user “has permission to modify a machine account (up to 10 machines) and as its owner, they also have the permissions to edit its sAMAccountName attribute,” Microsoft explains.

[ READ: PoC Exploit Published for Latest Microsoft Exchange Zero-Day ]

Advertisement. Scroll to continue reading.

Also a security bypass flaw, CVE-2021-42287 affects the Kerberos Privilege Attribute Certificate (PAC), also leading to domain controller impersonation. The vulnerability results in the Key Distribution Center (KDC) creating service tickets with higher privilege levels than those of the domain account.

During authentication using Kerberos, Ticket-Granting-Ticket (TGT) and the Ticket-Granting-Service (TGS) are requested from KDC. If the account for which TGS was requested could not be found, KDC would append a trailing $ to attempt to find it again.

“For example, if there is a domain controller with a SAM account name of DC1$, an attacker may create a new machine account and rename its SAM account name to DC1, request a TGT, rename it again for a different name, and request a TGS ticket, presenting the TGT he has in hands,” Microsoft notes.

Thus, with the lookup for DC1 failing, the KDC will attempt to find the machine trailing $, and “will issue the ticket using the privileges of DC1$.”

An attacker in the possession of domain user credentials can combine the two vulnerabilities and exploit them to gain domain admin privileges.

Microsoft has published a guide to help organizations identify any suspicious behavior related to the exploitation of these vulnerabilities by detecting abnormal device name changes and comparing them to a list of domain controllers in the target environment.

“As always, we strongly advise deploying the latest patches on the domain controllers as soon as possible,” Microsoft notes.

On November 14, the company released an out-of-band update to address a series of non-security issues related to applying the November 9 security updates.

Related: Zero-Days Under Attack: Microsoft Plugs Exchange Server, Excel Holes

Related: Microsoft Patches 67 Security Flaws, Including Zero-Day Exploited by Emotet

Related: Windows URI Handling Flaw Leads to Drive-by Code Execution

Written By

Ionut Arghire is an international correspondent for SecurityWeek.

Click to comment

Daily Briefing Newsletter

Subscribe to the SecurityWeek Email Briefing to stay informed on the latest threats, trends, and technology, along with insightful columns from industry experts.

SecurityWeek’s Threat Detection and Incident Response Summit brings together security practitioners from around the world to share war stories on breaches, APT attacks and threat intelligence.

Register

Securityweek’s CISO Forum will address issues and challenges that are top of mind for today’s security leaders and what the future looks like as chief defenders of the enterprise.

Register

Expert Insights

Related Content

Vulnerabilities

Less than a week after announcing that it would suspended service indefinitely due to a conflict with an (at the time) unnamed security researcher...

Data Breaches

OpenAI has confirmed a ChatGPT data breach on the same day a security firm reported seeing the use of a component affected by an...

Risk Management

The supply chain threat is directly linked to attack surface management, but the supply chain must be known and understood before it can be...

Vulnerabilities

The latest Chrome update brings patches for eight vulnerabilities, including seven reported by external researchers.

Vulnerabilities

Patch Tuesday: Microsoft warns vulnerability (CVE-2023-23397) could lead to exploitation before an email is viewed in the Preview Pane.

Vulnerabilities

Apple has released updates for macOS, iOS and Safari and they all include a WebKit patch for a zero-day vulnerability tracked as CVE-2023-23529.

IoT Security

A group of seven security researchers have discovered numerous vulnerabilities in vehicles from 16 car makers, including bugs that allowed them to control car...

Application Security

Drupal released updates that resolve four vulnerabilities in Drupal core and three plugins.